Gate Apron Rehab and Drainage Improvements - Denver International Airport

Abstract: In 2015, DEN initiated the Gate Apron Rehabilitation and Drainage Improvements (GARDI) Program to address heaving and settling pavements at the gate apron parking positions. The existing pavement at DEN is now more than 30 years old and has exceeded its originally intended 20-year design life. The differential movement of the gate apron pavement has created non-compliant drainage conditions where water and potentially jet fuel can drain toward the concourses instead of to the trench drains as originally designed. These conditions also contribute to safety hazards for apron workers such as trip hazards, spalling concrete, flooding of interior apron tenant spaces, and ponding on the pavement surface. The heaving and settling also has affected the underground utilities which, in some cases, have been damaged or rendered inoperable due to the differential movement of the pavement sections. These inoperable utilities can lead to costly emergency repairs and gate closures.

DEN is the 6th busiest airport in the world which includes 173 gates between the three concourses. The GARDI program ensures that the legacy gates from the original airport construction in 1995 are reconstructed to meet current engineering and technology aviation standards.

The GARDI scope includes removing the failing concrete panels, reconditioning and regrading the underlying subgrade as necessary to promote correct drainage, and eliminating historical issues that have promoted the differential movement in the area. The new GARDI pavement section includes a subgrade pavement drainage layer (cement treated permeable base) that will collect any water that leaks through the surface joints and will send the water to the underdrain piping system. The typical GARDI pavement section from bottom to top is 4” of Upper Select Fill, 12” of Cement Treated Soil Base Course, 3” of Asphalt Mix Pavement, 4” of Cement Treated Permeable Base (CTPB) Course, and 17” of Portland Cement Concrete Pavement.

In addition, all existing underground and surface utilities are replaced and relocated as necessary to support the gates operations. These utilities included are jet fuel pipe and hydrant pits, fire hydrants and supporting water vaults, storm drainpipe and manholes, sanitary sewer pipe and manholes, electrical conduit and handholes, cathodic pits and wiring, trench drains and underdrains, passenger loading bridges (PLBs), ground power units, and potable water cabinets.

There are a total of 102 gates from the original airport construction that have been identified for the GARDI program. As of October 2024, 39 gates have been reconstructed utilizing the GARDI treatment, totaling almost $230M, with three gates under construction and 60 gates remaining. Typically, these gates cost between $5M-$6M each, depending on the detailed scopes and schedules. This includes all design, project management, quality assurance, materials testing, project controls, construction, PLBs, and commissioning services for each individual construction package. Gates reconstructed at DEN as part of the GARDI program include 22 gates at Concourse B, both SE and NW quadrants, five gates at SE quadrant of Concourse A, and 12 gates on Concourse C East. Another 12 gates at Concourse A are currently in design for the GARDI program.